code: def test_dog():
      im = mh.demos.load("lena")
      im = im.mean(2)
      edges = mh.dog(im)
      assert edges.shape == im.shape
      assert edges.any()
      edges1 = mh.dog(im, sigma1=1.0)
      assert np.any(edges != edges1)
  
file_path: mahotas/mahotas/tests/test_edge.py
imports: from mahotas.edge import sobel
  import pytest
  import mahotas
  import numpy
label_desc: Use image node_id 7 for calling a global function with example usage: test_dog() without return types